Dual disc pressure release valve

Abstract

A pressure reducing control valve assembly for feeding an aeration fluid stream to a flotation tank includes a pair of overlapping discs, one having a central opening and affixed to an end of a tube, and the other imperforate and outwardly movable away from the surface of the fixed disc to define a valve opening having a predetermined land width. Optimum size of air bubbles for the objective desired is obtained by controlling the dimensions of a shear zone established by the land width within which the fluid stream is intensely turbulent for a short period of time, thereby causing air bubbles to form and then be discharged immediately into the liquid within the tank without having had time to coalesce.

What is claimed is: 
     
       1. In a flotation unit having a pressure reducing control valve assembly for supplying a flotation tank with an aeration fluid stream, the improvement wherein said valve assembly comprises an elongated inlet tube of a predetermined inner diameter, a fixed annular valve plate extending transversely at a terminal end of said tube and having an axial opening, a transversely extending imperforate disc valve movable toward and away from an outer surface of said valve plate respectively between valve closing and valve opening positions, said disc valve having an inner surface overlapping with said outer surface to define a valve land width, which establishes the length of a shear zone across which a pressure drop occurs, and means supporting said valve disc for axially shifting said disc to adjust the extend of said valve opening position, the ratio of the extend of said valve opening position to said land width being not greater than 1.0, whereby a predetermined size of air bubbles is controlled by said shear zone within which the fluid stream is intensely turbulent for a predetermined short period of time thereby causing air bubbles to form and then be discharged into liquid within said tank without having had time to coalesce. 
     
     
       2. In the flotation unit according to claim 1, wherein said opening of said valve plate is of a size substantially equal to said inner diameter for determining the extent of said land width and thus the extned of said shear zone. 
     
     
       3. In the flotation unit according to claim 1, wherein said valve plate and said disc have unequal outer diameters for determining the extent of said land width and thus the extent of said shear zone. 
     
     
       4. In the flotation unit according to claim 1, wherein said inner and outer surfaces lie parallel to one another at said inner shear zone, a portion of said inner surface between said shear zone and said supporting means being smoothly contoured, and a confronting inner surface at said terminal end of said tube having a contour matching said inner surface position, whereby the fluid stream is streamlined to thereby minimize turbulence at the entrance to said shear zone. 
     
     
       5. In the flotation unit according to claim 1, wherein portions of said inner and outer surfaces lie outwardly of said shear zone and diverge outwardly toward the edges of said valve plate and said disc valve, whereby the fluid flow is caused to change upon exiting said shear zone. 
     
     
       6. In the flotation unit according to claim 1, wherein said inner and outer surfaces are parallel at said shear zone and together taper toward an outer surface of said disc valve to thereby control the direction of flow. 
     
     
       7. In the flotation unit according to claim 1, wherein said inner and outer surfaces at said shear zone diverge outwardly toward the edges of said valve plate and said disc vavle, whereby exit flow from said shear zone is multi-directional. 
     
     
       8. In the flotation unit according to claims 1, 2, 3, 4, 5, 6 or 7, wherein said shifting means comprises an elongated rod coaxial with said tube and being axially movable relative thereto, said valve disc being mounted at one end of said rod means at the opposite end of said rod for axially moving same. 
     
     
       9. The the flotation unit according to claim 8, wherein said rod is coaxially supported within said tube by means of a bearing element through which said rod extends. 
     
     
       10. In the flotation unit according to claim 1, wherein said means at said opposite end comprises an internally threaded support element engaging a threaded portion of said rod.